1. Field of the Invention
This invention pertains generally to seed dispensers for planters and more specifically to air planters.
2. Description of the Prior Art
A conventional dispenser for an air planter may be of the type shown in U.S. Pat. No. 3,848,552 issued Nov. 19, 1974 to Jack L. Bauman et al. and assigned to subject assignee. The dispenser described therein, has been in successful commercial use for a substantial number of years but nevertheless has disadvantages that have been reduced, but never substantially eliminated.
For example, a generally rigid vertical wall is provided in the dispenser against which is rotatably mounted an open ended rotating drum having pocket surrounded rod openings therethrough around its periphery for seeds with the seeds being supplied from a lower chute extending through the wall into the interior of the drum from a suitable seed hopper. A blower attached to the same wall via an opening therethrough, supplies compressed air into the interior of the drum and as the drum is rotated, via a ground wheel planter drive which relates seed spacing to ground travel, holds the seed by escaping air in the openings until a discharge area is reached. A cut-off brush before the discharge area removes excess seeds (over one) from each pocket. At the top center (12 o'clock) position or discharge area, a rubber roller riding on the drum exterior periphery closes each hole and gravity causes the seed to drop into a seed tube located below the roller, wherein the air escaping in the drum moves the seed through the tube and out through the drum via a tube opening in the stationary plate to a furrow.
A disadvantage of the above structure is that each seed pocket, now empty after seed discharge remains so until the drum revolves to the lower position of its travel wherein seeds from the hopper fill the pockets again. Air, however, is lost out the empty pockets. The air loss is particularly pronounced, with 144 holes per row drum for soy beans compared to corn (24 holes per row). Air saver shields have reduced this air loss but only partially. Due to air loss only drums with 144 holes per row can be used; as a consequence soybeans can only be planted at 4.75 mph to desired population seed rates (12 seeds per foot) rather than maximum planter speed of 8 mph for corn.
More important than the air loss, however, is the rpm sensitivity of the seed release. Generally the seed drum r.p.m. cannot exceed 35 rpm to avoid not filling the pockets in the drum to control population. It is to be noted that on start up and slow down of the tractor and therefore planter speed, the related drum rpm changes. This affects the inertial force the drum imparts to the seed, hence, at the 12 o'clock or top center drum position, while the force of gravity downward is constant, the resultant seed path changes and the seed frequently ricochets in the tubes affecting the desired uniform seed spacing in the furrow. Also the current round interior seed tube can allow the seed to spiral as they contact the tube walls which also affects seed spacing.